Diesel engines, because of the way they operate, emit soot particles or very fine droplets of condensate or a conglomerate of the two (particulates) as well as typical harmful gasoline engine exhausts (i.e., HC and CO). These “particulates” (herein Diesel soot), are rich in condensed, polynuclear hydrocarbons, some of which may be carcinogenic.
As the awareness of the danger Diesel soot presents to health collides with the need for greater fuel efficiency that Diesel engines provide, regulations have been enacted curbing the amount of Diesel soot permitted to be emitted. To meet these challenges, soot filters have been used. The filters have had many configurations as exemplified by GB 1,014,498 and U.S. Pat. No. 4,828,807. The most common and useful filters have tended to be porous ceramic honeycombs that have plugged channels such that the exhaust gas must enter a channel and pass through the wall of the channel as exemplified by U.S. Pat. No. 4,329,162.
Ceramic honeycombs have been made from smaller segements to make larger devices such as flow through catalysts (3-way), heat regenerators and Diesel filters as exemplified by U.S. Pat. Nos. 4,304,585; 4,333,518; 4,381,815; 4,953,627; 5,914,187; 6,669,751; 6,984,253; 7,056,568 and U.S. Pat. Publ. 2006/029333.
In particular, U.S. Pat. No. 6,669,751 and U.S. Pat. Publ. 2006/029333, describe cementing, for example, filter segments of square cross-section wherein the outer corners have a straight chamfer or round corner having a radius of curvature of 0.3 mm-2.5 mm. The latter further teaches that the corner may have a straight chamfer and and round corner with the aforementioned radius of curvature. Such chamfers were described as being useful to improve strength (thermal shock resistance). However, these corners suffer from limited flexibility in wall thickness at the corner, fails to take into account of damage that may occur upon handling (i.e., still has sharp corners from chamfers, inability to adequately hard coat dies in the corners and inability to accurately reproduce the intended shape as described by U.S. patent Pub. 2006/029333, which may cause stress concentration causing edge chipping etc).
What is needed is a Diesel particulate filter that avoids one or more of the problems of the prior art such as one or more of those described above.